Metallic pipes used in pipelines for transporting fluids, gasses, etc. and transmission lines are found abundantly throughout the world. These metallic pipes or conduits, such as ductile iron pipes, are used as water mains and the like. While effective, metallic pipelines have a corrosion problem, when immersed in an electrolyte. A current is created between the metal and the electrolyte causing ions to leave the metal. Many untold miles of pipelines are buried in soil, which is an effective electrolyte. Over time, the metal of the pipeline can be weakened, resulting in leaks and breakages. Various forms of cathodic protection are employed to slow or if possible, halt the corrosion of pipelines. Corroding metal is anodic relative the cathodic or non-corroding areas. Cathodic protection simply couples a metal of higher potential to the metal of the pipeline, creating an electrochemical cell in which the metal of the pipeline becomes a cathode and no longer loses ions. In theory, this practice is a complete cure to corrosion. However, in application many problems can occur, including expense and technical difficulties. However, it is clear that knowing the level of protection, or lack thereof is important.
The primary measurement to determine the effectiveness of cathodic protection is a pipe-to-soil potential criterion. This technique measures the voltage difference between the pipeline and a reference electrode, typically a copper-copper sulfate electrode, placed in or on the electrolyte near the structure. Test stations are often periodically placed along the pipeline to measure the potential of the pipeline and the surrounding soil. These test stations, however, are generally widely separated, and do not give measurements for areas between the stations. This problem has been partially overcome by the use of hand held probes and a wire dispenser carried by a backpack. The wire is coupled to a test station to maintain a measurement of the potential of the pipeline, while the hand probe is periodically placed in contact with the ground to obtain the soil potential, which can then be compared to the pipe potential. This gives more measurements than the test stations, but can be time consuming and tiring to the individual performing the measurements.
It would be highly advantageous, therefore, to remedy the foregoing and other deficiencies inherent in the prior art.
Accordingly, it is an object of the present invention to provide a new and improved method and apparatus for measuring pipe-to-soil potential.